This ongoing research program is organized into three distinct but related areas. The general aim of the first area is to elucidate and describe selective attentional mechanisms as they operate in visual information processing. Ongoing and proposed research is directed toward attention effects at early levels in stimulus processing, stimulus selection and the role of competing responses, sustained attention, and the spatial characteristics of the distribution of attentional resources in the visual field. Among the methodologies used, response competition paradigms, cost benefit analysis, and reaction time measures play a major role. A second area of research is to refine a new set of measures that analyze the microstructure of the responses that are used to signify choice in reaction time tasks. In recently completed pilot studies, these measures have shown high promise of reflecting differences in information processing that are not revealed in the usual latency measures. A third research direction uses a response competition paradigm to determine the extent and nature of the relationships and content that is retrieved upon semantic processing of a word.